The studies in this project have two major goals: 1) to understand the anatomical aspects of the temporal bone, both normal and pathological, that are relevant to cochlear implantation, and 2) to develop theoretical computer-based models from three-dimensional reconstructions of the cochlea in order to further our understanding of the physical and physiological mechanisms underlying the electrical excitation of auditory nerve fibers through cochlear implants. Three-dimensional reconstructions of normal human, cat and rat cochleas will form the basis of electro-anatomical models of potential distributions and patterns of current flow that occur when the cochlea is electrically stimulated. The model will be implemented for the cat and rat, as well as the human, to permit some forms of testing that are not possible in humans; e.g., recording from single auditory nerve fibers, and to study the perturbations resulting from experimentally induced cochlear pathologies. The development of single-fiber models will be integrated with the electro-anatomical models to enable predictions of auditory nerve spike discharge patterns across the fiber array. Of direct relevance to this theoretical effort is an investigation of the spatial relationships between spiral ganglion cells in Rosenthal's canal and their innervation of the organ of Corti, particularly in the apical turn where direct radial projections are unlikely. Another important aspect of temporal bone anatomy to be addressed in this project concerns the histopathology that results from cochlear implantation, which will be analyzed by reconstructing implanted cochleas form deceased patients. These cochlea will be sectioned with the implant in place, which will permit accurate localization of the electrodes. Patterns of spiral ganglion cell degeneration will be studied in an animal model to shed light on the degeneration process and in human material to relate the effects of degeneration to speech reception with cochlear implants.